A “power takeoff” device, commonly referred to simply as a “PTO,” is typically mounted to a transmission with a gasket positioned between the PTO housing and the transmission housing. Mounting the PTO to the transmission, which is typically accomplished using bolts, commonly requires mating adjacent flanges of the PTO and the transmission with a gasket therebetween in order to seal the bolted joint. Selection of a proper gasket thickness can control the PTO gear center distance, which affects “backlash” and gear interference between the meshing PTO and transmission gears.
Backlash, sometimes called “lash” or “play,” is the lost motion between the respective mating gear teeth of the PTO and the transmission. Backlash can also be described as the clearance between such mating gears, or as the amount of lost motion due to clearance or slackness when movement is reversed and contact between the respective gears is re-established. Backlash may be measured in different manners, such as along the line of action or on the pitch cylinder of the gears. Factors affecting the extent of backlash in meshing gears include the actual center distance at which the gears operate and the manufactured tooth thickness. Excessive backlash can cause rattle noise, especially in systems that may be prone to rattle, and excessive wear. On the other hand, an absence of any backlash (tightly meshed gears) can cause excessive noise, such as whining, and excessive wear.
Selection of a proper gasket thickness can play an important role in properly coupling a PTO to a transmission. Excessive gasket thickness can result in too much backlash, which as noted can cause excessive rattle and wear on the gears. Insufficient gasket thickness will allow the PTO center distance to be reduced to a point where gear interference may occur, which can occur unintentionally during mounting, especially in situations where it is easy to force the gears together such as when a PTO is bolted to the transmission. Gear interference can cause noisy operation or, in more severe situations, result in catastrophic failure of the gears, the PTO and/or the transmission.